Abstract
The larvacean Oikopleura dioica is a planktonic chordate and an emerging model organism with a short life cycle of 5 days that belongs toTunicata (Urochordata), the sister clade of vertebrates. It is characterized by the rapid development of a tadpole-shaped body. Organ formation in the trunk proceeds within 7 h after the hatching of the tailbud larvae at 3 h after fertilization (hpf) and is completed at 10 hpf, giving rise to fully functional juveniles as miniature adult form. Serial block face scanning electron microscopy was used to acquire ~ 2000 serial transverse section images of a 3 hpf larva and a 10 hpf juvenile to characterize the structures and cellular composition of the trunk and organs using 3D images and movies. Germ cells were found to fuse and establish a central syncytial cell in the gonad as early as 10 hpf. Larval development gave rise to functional organs after several rounds of cell division through trunk morphogenesis. The feature would make O. dioica ideal for analyzing cellular behaviors during morphogenetic processes using live imaging. The detailed descriptions of the larvae and juveniles provided in this study can be utilized as the start and end points of organ morphogenesis in this rapidly developing organism.
Highlights
The larvacean Oikopleura dioica is a planktonic chordate and an emerging model organism with a short life cycle of 5 days that belongs toTunicata (Urochordata), the sister clade of vertebrates
The larvacean Oikopleura dioica is a planktonic chordate with a short life cycle of 5 days
The morphogenesis of various trunk organs is completed at 7 h of larval development
Summary
The larvacean Oikopleura dioica is a planktonic chordate and an emerging model organism with a short life cycle of 5 days that belongs toTunicata (Urochordata), the sister clade of vertebrates It is characterized by the rapid development of a tadpole-shaped body. Organ formation is completed and fully functional juveniles are formed at 10 hpf, at which point they start feeding and are considered to be miniature adult forms. At this stage, the cell division of most somatic cells, except for those in the digestive organs, ceases and the cells start to increase their size via endoduplication, culminating in the development of sexually mature adults on the fifth d ay[4]. Detailed descriptions of the structures and cellular compositions of the larvae and juveniles provide the start and end points of organ morphogenesis in this rapidly developing organism. The descriptions are useful for interpreting the results of gene knockdown/knockout experiments using this organism, which evolved a body with extremely simplified morphology and small cell number
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